1. Field of the Invention
This invention relates generally to systems and methods for semiconductor fabrication, and more particularly concerns systems and methods for purging a modular isolation chamber such as a standard mechanical interface box or pod used for storing or transporting semiconductor manufacturing materials, to desired levels of relative humidity, oxygen, or particulates.
2. Description of Related Art
A modular isolation chamber such as a standard mechanical interface (SMIF) box, or pod, typically provides a microenvironment to isolate and control the environment surrounding a wafer, cassette of wafers or substrates used in manufacturing integrated circuits, during storage, transport and processing of the materials. Processing of such materials traditionally has been carried out in a particulate free environment generally known as a xe2x80x9cclean roomxe2x80x9d. However, maintenance of such xe2x80x9cclean roomsxe2x80x9d in a contaminant free state can require a great deal of care and effort, particularly during processing of the materials.
In one conventional system in which a SMIF system is used to replace a traditional clean room, filtered air is circulated in the SMIF box, and still air is used to achieve cleanliness in the SMIF box. A particle-free dockable interface for linking together two spaces each enclosing a clean air environment includes interlocking doors on each space that fit together to trap particles which have accumulated from the dirty ambient environment on the outer surfaces of the doors. A processing apparatus and technique is also known for thermal processing in the manufacture of semiconductor devices, to prevent outside air from entering a reaction tube. Loading and unloading an object to be processed is typically effected by an insertion jig outside a heating section, to prevent outside air from entering the heated processing chamber.
While such systems can control the level of particulates in a SMIF box, the presence of oxygen can also degrade the surface of semiconductor materials. In one conventional process for preventing the formation of native oxides on the surface of semiconductor materials, silicon nitride layers are formed on silicon substrates. Purge systems are also known, such as one in which a movable cantilevered purge system provides for a wafer load position, a wafer purge position, and a wafer process position. A purge injector and return exhaust tube are provided in an elephant tube which provides for access to wafer loads. In another known system, the manufacturing materials are subjected to cold-nitrogen purge cycles, and particles and particle-generated defects during gas phase processing such as during deposition are decreased by controlling particle transport mechanisms, such as by applying low level radiant energy during cold nitrogen purge cycles.
The presence of humidity in a SMIF box can also be undesirable. One conventional method and apparatus for cleaning integrated circuit wafers utilizes dry gases. At least one of the gases is excited by passing the gas through a microwave plasma generator or by heating the wafer, exciting the gases near the surface of the wafer, causing chemical reactions similar to those induced by ionization of nongaseous cleaning materials in water. After an etching period, the etching chamber is purged by inert gas, such as nitrogen, which helps carry away the remaining reacted contaminants, which can include vaporous halogens or radicals that can be present after conventional processes, such as chlorine, bromine, arsine, silane, and the like.
However, there remains a need for a system and method of purging SMIF pods to consistently maintain desired levels of relative humidity, oxygen, or particulates while the pods are otherwise not required, such as while waiting for a next production station or step in a fabrication facility. These periods have been estimated to be about six minutes to several hours long. Ideally, the SMIF pod should be completely purged to desired levels of relative humidity, oxygen, or particulates in a period of about 6 minutes or less. The present invention meets these needs.
Briefly, and in general terms, the present invention provides for an improved system and method for purging a SMIF pod to desired levels of relative humidity, oxygen, or particulates. In one preferred embodiment, the SMIF pod includes an inlet port and an outlet port, each including a check valve filter assembly, for a clean, dry gaseous working fluid that is used to provide controlled low levels of moisture, oxygen, and particulate content around the materials contained in the SMIF pod. The SMIF pod inlet port is connected with a gaseous working fluid source, and the outlet port is connected with an evacuation system. The integral directional flow check valves operate at very low pressure differentials (such as less than 10 millibar).
The method of the invention also provides for improvements to a purge process by drying of purge gas by exposure to a desiccant; heating the purge gas to temperatures above 100xc2x0 C., but below the thermal sensitivity of the pod, i.e., 105 to 120xc2x0 C.; and testing the pre-treated gaseous working fluid for baseline constituent levels prior to introduction into a SMIF Pod. In another aspect of the invention, an improved inlet flow of the purge gas is provided, by maintaining the purge gas velocity throughout the gas stream in the pod at a laminar flow velocity, below sonic flow velocity, to prevent formation of undesirable vortices that may trap moisture or particles, and to encourage laminar flow inside the pod. In another embodiment, flow of purge gas inside the SMIF pod is directed towards the product using one or more nozzle towers to encourage laminar flow inside the pod. One or more outlet towers, having a function similar to that of the inlet tower, may also be provided to encourage laminar flow inside the pod. In another embodiment, integrated towers are provided to direct and disperse flow of the gaseous working fluid throughout the pod envelope. A molecular contamination control base unit on which the SMIF pod can be mounted can also include features for improvement of the purging of the environment in the pod. In another aspect of the method of the invention, mass flow control can be used to ramp the gas flow rate up and down in a controlled manner to avoid generation of particles due to xe2x80x9crattlingxe2x80x9d of the wafers in the SMIF pod.
These and other aspects and advantages of the invention will become apparent from the following detailed description, and the accompanying drawings, which illustrate by way of example the features of the invention.